In the steel industry, it is conventional practice to transfer the molten steel produced in a furnace to a steel ladle, from which the steel is teemed (poured) into ingots or continuous caster tundishes. The ladle is conventionally equipped with a valve in its bottom, which is used to control the flow of molten steel out of the ladle. A conventional valve employed in such ladles consists of a stopper rod assembly, comprising a vertical, refractory-covered rod extending upwardly above the top of the ladle, the bottom end of the rod being adapted to block the bore of a refractory nozzle positioned in the bottom of the ladle. Before the ladle is filled with molten steel, the lower end of the stopper rod is positioned into sealing engagement with the nozzle in the bottom of the ladle. After the ladle is filled, the flow of steel from the ladle is initiated by lifting the stopper rod by suitable means out of sealing engagement with the nozzle, permitting the steel to flow as desired.
In order to prevent leakage of molten steel out of the nozzle through the stopper rod assembly prior to teeming, which might occur as a result of an imperfect seal or of jarring of the ladle during operation, a suitable procedure has been to insert a bag enclosing a quantity of a finely divided refractory material, such as sand, into the open bore of the nozzle below the lower end of the stopper rod and to keep the bag in place in the bore of the nozzle by means of an external plug. If any molten steel escapes past the sealing end of the stopper rod into the nozzle, it contacts the refractory material and freezes in place. In order to support the bag of refractory material in place within the bore of the nozzle, tapered wooden or metal plugs making a friction fit in the bore of the nozzle have been used. Both of these types of plugs have disadvantages in use. A wooden plug is subject to being loosened by jarring or other impact or to charring as a result of the high temperatures typically existent during the operation of such ladles. On the other hand, a tapered metal plug, driven into the bore of the nozzle with sufficient force to ensure a firm engagement, has a tendency to crack the refractory material near the tip of the nozzle.